This invention relates broadly to the boring of a hole through the wall of a tube from the inside of the tube outwardly perpendicular to a longitudinal axis of the tube. More particularly, this invention relates to drilling through an oil or gas well casing perpendicular to the longitudinal axis of the casing and laterally into the earth strata surrounding the well casing.
Oil and gas wells are drilled vertically down into the earth strata with the use of rotary drilling equipment. A tube known as a casing is placed down into the well after it is drilled. The casing is usually of made of mild steel and is in the neighborhood of 4.5 inches to 8 inches in external diameter (4 inches in internal diameter and up) and defines the cross-sectional area of the well for transportation of the oil and gas upwardly to the earth surface. However, these vertically extending wells are only useful for removing oil and gas from the terminating downward end of the well. Thus, not all of the oil and gas in the pockets or formations in the surrounding earth strata, at the location of the well depth, can be removed. Therefore, it is necessary to either make additional vertical drillings parallel and close to the first well, which is costly and time consuming, or to provide some means to extend the original well in a radial direction relative to the vertical longitudinal axis of the casing horizontally into the surrounding earth strata.
The most common means for horizontal extension of the well has been to drill angularly through the well casing at a first 45xc2x0 angle for a short distance and then to turn the drill and drill at a second 45xc2x0 angle thereby making a full 90xc2x0 angular or horizontal cut from the vertically extending well. These horizontal drills have proved useful for extending the well horizontally but have proved to be relatively expensive.
Another solution to the problem is disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056, both of which are hereby incorporated by reference herein as if fully set forth in their entirety. In these patents there is disclosed an apparatus comprising an elbow, a flexible shaft or so-called xe2x80x9cflex cablexe2x80x9d and a ball cutter attached to the end of the flexible shaft. The elbow is positioned in the well casing, and the ball cutter and flexible shaft are passed through the elbow, turning 90xc2x0. A motor rotates the flexible shaft to bore a hole in the well casing and surrounding earth strata with the ball cutter. The flexible shaft and ball cutter are then removed and a flexible tube with a nozzle on the end thereof is passed down the well casing, through the elbow and is directed out of the casing through the hole therein. Water pumped through the flexible tube exits the nozzle at high speed and bores further horizontally into the earth strata.
Prototype testing of the device disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056 has proven less than satisfactory. In particular, a number of problems plague the device disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056. For example, the disclosed ball cutter is inefficient at best and ineffective at worst in cutting through the well casing. The inherent spherical geometry of a ball cutter causes it xe2x80x9cwalkxe2x80x9d or xe2x80x9cchatterxe2x80x9d during rotation as it attempts to bore through the well casing which greatly increases the amount of time required to bore through the casing. Ball cutters are best utilized for deburring, and/or cutting a radius in an existing hole or slot for example, and are simply not suitable for drilling holes.
Another problem is the torsional flexibility of the flexible shaft or flex cable. Rather than transmitting rotational displacement to the ball cutter at 100% efficiency the flex cable tends to xe2x80x9cwind upxe2x80x9d or exhibit xe2x80x9cbacklash,xe2x80x9d thus reducing the already inefficient cutting efficiency of the ball cutter even more.
Yet another problem is the tendency of the elbow to back away from the hole in the casing during drilling with the ball cutter. Such backing away causes the elbow outlet to become misaligned with the hole in the casing thereby preventing smooth introduction of the nozzle and flexible tube into the hole in the casing.
Still another problem is the large amount of torsional friction generated between the elbow passageway and the flex cable which of course increases the horsepower requirements of the motor required to rotate the flex cable. The addition of balls, separated by springs, to the flex cable, in an effort to alleviate the resistance of the apparatus to being rotated, has not remedied this problem.
A further problem is the closed nature of the apparatus of U.S. Pat. Nos. 5,413,184 and 5,853,056, which prevents its being taken apart, inspected, cleaned and repaired as needed.
The present invention overcomes the deficiencies of the apparatus disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056. The present invention is apparatus for boring a hole from an inside of a tube outwardly perpendicular to a longitudinal axis of the tube. The apparatus comprises a drill shoe having a longitudinal axis and being positionable in the tube, the shoe having an inlet, an outlet perpendicular to the shoe longitudinal axis and a passageway connecting the inlet and outlet, a torsional load transmitting element having no torsional flexibility in relation to its bending flexibility, having a longitudinal axis and being disposed in the passageway, the torsional load transmitting element being movable relative to itself about first and second perpendicular axes both of which are perpendicular to the longitudinal axis of the torsional load transmitting element, a hole saw connected to one end of the torsional load transmitting element and a motor rotatably connected to the other end of the torsional load transmitting element. Rotation of the torsional load transmitting element by the motor rotates the hole saw to bore through the tube from the inside of the tube outwardly perpendicular to the longitudinal axis of the tube.
Preferably the torsional load transmitting element is freely movable relative to itself about the first and second perpendicular axes. Further preferably the torsional load transmitting element is pivotable relative to itself about the first and second perpendicular axes. Still further preferably the torsional load transmitting element is freely pivotable relative to itself about the first and second perpendicular axes.
The torsional load transmitting element is preferably a plurality of interconnected universal joints having a longitudinal axis and being disposed in the passageway, adjacent ones of the universal joints being pivotable relative to one another about first and second perpendicular axes both of which are perpendicular to the longitudinal axis of the plurality of interconnected universal joints. Adjacent ones of the universal joints are preferably pivotable relative to one another by at least about 35xc2x0.
The apparatus may further comprise a drill bit connected to the torsional load transmitting element centrally of the hole saw.
The apparatus may further comprise a biasing element mounted to the shoe and adapted to bias the outlet of the shoe against the tube.
The apparatus may further comprise a detent mechanism operable between the shoe and the motor to prevent the motor from rotating relative to the shoe.
The drill shoe is preferably fabricated in halves.
The tube is preferably a well casing, for example an oil well casing or a gas well casing.